Golf ball

ABSTRACT

The present invention provides a golf ball having excellent flyer resistance at a shot on the rough, and having high rebound characteristics and excellent flight performance. The present invention relates to a golf ball comprising a core having a single-layered structure or a multi-layered structure and a cover covering the core, wherein the cover has a complex elastic modulus at −10° C. of 20 to 150 MPa and loss tangent (tan δ) at −10° C. of not less than 0.05, as determined from temperature-dependent curves of the complex elastic modulus and tan δ obtained by dynamic viscoelastic measurement at a frequency of 10 Hz, a dynamic strain of 5% and a heating rate of 4° C./min.

FIELD OF THE INVENTION

[0001] The present invention relates to a golf ball having excellentspin performance. More particularly, it relates to a golf ball havingexcellent flyer resistance at a shot on the rough, and having highrebound characteristics and excellent flight performance.

BACKGROUND OF THE INVENTION

[0002] Solid golf balls, such as a two-piece golf ball or three-piecegolf ball, and thread wound golf balls have been used for round games.The solid golf ball consists of a solid core of integrally molded rubbermaterial comprising polybutadiene as a main component and a cover ofthermoplastic resin (e.g. ionomer resin) covering on the solid core. Thethread wound golf ball consists of a solid or liquid center, a threadrubber layer formed by winding thread rubber in a stretched state aroundthe center, and a cover of ionomer resin or balata etc. covering on thethread wound layer.

[0003] A golf ball is often placed in a rough or tall lawn by accidentin a round play. When one hit the ball from the lawn, a phenomenoncalled flyer easily occurs, that is, backspin amount is small and balltrajectory is high because of the presence of the lawn between the golfclub and the golf ball. The flyer phenomenon would bring aboutdifficulty in controlling the ball trajectory and spin amount andespecially causes poor controllability at approach shots, which has beena problem to be solved. The phenomenon occurs regardless of the solidgolf ball or thread wound golf ball, and many golf players are troubledwith it.

[0004] It has been found in studying the flyer phenomenon with respectto types of covers of golf balls that the flyer occurs more easily onionomer-cover golf balls than balata-cover golf balls. In case of thegolf ball using balata cover, it has been known that the flyer isdifficult to occur and the controllability of spin is excellent, but therebound characteristics of the cover material is poor and the cutresistance is poor. On the other hand, the ionomer resin cover has highelastic modulus and excellent rebound characteristics, but the resultinggolf ball having ionomer cover has small spin amount and poorcontrollability.

[0005] In order to solve the flyer problem and provide a golf ballhaving excellent rebound characteristics, the present inventors haveproposed a selection of a cover material for a golf ball having acomplex elastic modulus of 50 to 1500 kgf/cm² (about 5 to 150 MPa) at−10° C. obtained by dynamic viscoelastic measurement and a resilience ofnot less than 50% obtained by a tripsometer (Japanese Patent Kokaipublication No. 305115/1998). However, in the golf ball using the covermaterial, sufficient flyer resistance has not been obtained, becausehigher performance has been required for current golf balls for roundgames.

OBJECTS OF THE INVENTION

[0006] A main object of the present invention is to provide a golf ballhaving excellent flyer resistance at a shot on the rough, and havinghigh rebound characteristics and excellent flight performance.

[0007] According to the present invention, the object described abovehas been accomplished by adjusting a complex elastic modulus and tan δof cover to specified ranges, thereby providing a golf ball havingexcellent flyer resistance at a shot on the rough, and having highrebound characteristics and excellent flight performance.

SUMMARY OF THE INVENTION

[0008] The present invention relates to a golf ball comprising a corehaving a single-layered structure or a multi-layered structure and acover covering the core, wherein the cover has a complex elastic modulusat −10° C. of 20 to 150 MPa and loss tangent (tan δ) at −10° C. of notless than 0.05, as determined from temperature-dependent curves of thecomplex elastic modulus and tan δ obtained by dynamic viscoelasticmeasurement at a frequency of 10 Hz, a dynamic strain of 5% and aheating rate of 4° C./min.

[0009] In the cover material which has been proposed by the presentinventors as described above (Japanese Patent Kokai publication No.305115/1998), a complex elastic modulus measured at specifiedtemperature, frequency and dynamic strain is used as a factor showingdynamic hardness, and is adjusted to specified ranges. This techniqueresides in specifying the dynamic hardness at conditions of approachshots, such as room temperature, high frequency and large deformationamount, and selecting some factors for easily applying spin on balls.

[0010] The present inventors have further studied cover materials inmore detail, and have found that there are golf balls which have or havenot sufficient flyer resistance in the golf ball using the covermaterial having such properties as described in our previous invention.This is because the flyer occurs under the specific conditions, whichhave not considered yet. That is, the behavior of the golf ball when hitin the state of putting the grass between the golf club face and thegolf ball is not explained only by the dynamic hardness based on thedeformation condition at approach shot. It is required to reconsider howto prevent the flyer from occurring, particularly remarkable propertiesof the golf ball in the special state described above.

[0011] In the golf ball having excellent flyer resistance, it isrequired to have sufficient backspin amount when hit in the state ofputting the grass between the golf club face and the golf ball. That is,it is difficult to give the golf ball a spin if friction force is notapplied between the golf club face and the surface of the golf ball inthe state of putting the grass there. The flyer resistance can beimproved by maintaining the friction force when hit in the state ofputting the grass between the golf club face and the golf ball.Therefore, it is required to remark the properties connected with thefriction force.

[0012] Polymer materials used for the cover of golf balls generally haveviscoelasticity, that is, have both elasticity and viscosity. Theelasticity mainly controls properties such as elastic modulus, flexuralstrength, hardness and the like of the materials, and the viscositymainly controls properties such as impact strength, friction force(coefficient of friction) and the like of the materials.

[0013] The present inventors have studied the flyer resistance andproperties of the cover materials, and have remarked loss tangent “tanδ”, which represents mechanical damping, in addition to the complexelastic modulus as a factor for representing dynamic hardness. Thecomplex elastic modulus E* and tan δ are represented by the followingtwo formulae:

E*=(E′ ² +E″ ²)^(½)

tan δ=E″/E′

[0014] (wherein E′ is storage elastic modulus, and E″ is loss elasticmodulus.). The δ is an angle, which represents a time lag between stressapplied and strain. The loss tangent (tan δ), which is also calledcoefficient of loss, represents ability of dissipating the stressapplied on the material as thermal energy, that is, energy loss.Therefore, when the value of tan δ is large, the value of properties,which depend on viscosity, such as impact strength, friction force andthe like is large.

[0015] The friction force F_(f) is generally represented by thefollowing formula:

F _(f) =F _(a) +F _(h) +F _(b)

[0016] (wherein F_(a) is adhesion friction force, F_(h) is hysteresisloss friction force, and F_(b) is abrasion friction force.) Assumingthat a bonding strength in a level of molecular rises at the interfacebetween the golf club face and the surface of golf ball, the adhesionfriction force is a force that is necessary to shear destruct thebonding strength. The adhesion friction force depends on the contactsurface, and is large when the contact area is large.

[0017] The cover on the surface of golf ball repeats compressiondeformation and recovery behavior along the unevenness of the golf clubface contacting with the golf ball at the time of hitting, but energyloss occurs in the cover and is compensated by work from the stressapplied from the outer, which work arises hysteresis loss frictionforce. The hysteresis loss friction force is friction force, which isgiven by deformation. Abrasion friction force also arises between a golfball surface and a surface of a golf club, but is not considered for thepresent invention because no abrasive force applied from the golf ballto the golf club.

[0018] The adhesion friction force has large effect on the golf ballwhen usually hit in the state of putting no grass between the golf clubface and the golf ball. On the other hand, the hysteresis loss frictionforce has large effect on the golf ball when hit in the state of puttingthe grass between the golf club face and the golf ball. The lower thehardness, the larger the hysteresis loss friction force. When thehardness is in lower range, the larger the coefficient of loss (tan δ),the larger the hysteresis loss friction force. On the other hand, whenthe hardness is in higher range, the tan δ is small, and effectstherefrom is also small. Therefore it is required to use the covermaterial, of which the complex elastic modulus representing hardness issmall and the tan δ is large in order to improve the flyer resistance.

[0019] In the golf ball of the present invention, it is required for thecover to have a complex elastic modulus at −10° C. of 20 to 150 MPa andloss tangent (tan δ) at −10° C. of not less than 0.05, as determinedfrom temperature-dependent curves of the complex elastic modulus and tanδ obtained by dynamic viscoelastic measurement at a frequency of 10 Hz,a dynamic strain of 5% and a heating rate of 4° C./min. The complexelastic modulus is preferably not more than 100 MPa, more preferably notmore than 50 MPa. The tan δ is preferably not less than 0.07. However,when the complex elastic modulus is too small, or the tan δ is toolarge, the rebound characteristics, which are important factor, aredegraded. Therefore the complex elastic modulus is preferably not lessthan 30 MPa, and the tan δ is preferably not more than 0.3, morepreferably not more than 0.11.

[0020] The present inventors have found that the state of having highfrequency at room temperature when hitting the golf ball correlates withthe complex elastic modulus obtained by dynamic viscoelastic measurementat lower temperature of −10° C. and a frequency of 10 Hz fromtemperature-frequency conversion law. They have also found that thecomplex elastic modulus at −10° C. measured at a dynamic strain of 5%correlates with the occurrence of flyer by adjusting the dynamic strainto 5%, which is close to the deformation amount of the golf ball atapproach shot (Japanese Patent Kokai publication No. 305115/1998).

DETAILED DESCRIPTION OF THE INVENTION

[0021] In the detailed description of the present invention whichfollows, the golf ball of the present invention comprises a core and acover formed on the core. The golf ball of the present invention may beeither solid golf ball such as two-piece solid golf ball or thread woundgolf ball. The core for solid golf ball (solid core) may be the same onethat has been conventionally used, and may be obtained by mixing arubber composition using a mixer such as a mixing roll, and thenvulcanizing (crosslinking) or press-molding the rubber composition in agiven mold into a spherical form. The rubber composition comprises 10 to60 parts by weight of a vulcanizing agent (crosslinking agent), forexample, α,β-unsaturated carboxylic acid (such as acrylic acid,methacrylic acid, etc.) or a metal salt thereof, or a functional monomersuch as trimethylolpropane trimethacrylate, or a combination thereof;0.5 to 5 parts by weight of organic peroxides such as dicumyl peroxide,etc.; 10 to 30 parts by weight of filler such as zinc oxide, bariumsulfate and the like; optionally antioxidant, based on 100 parts byweight of a base rubber such as polybutadiene. The vulcanization may beconducted, for example, by press molding in a mold at 140 to 170° C. for10 to 40 minutes.

[0022] The core for thread wound golf ball (thread wound core) comprisesa center and a thread rubber layer formed by winding thread rubber in astretched state around the center, wherein the center may be eitherliquid center or solid center formed from rubber composition. The threadrubber can be of the same kind which has been conventionally used forthe thread rubber layer of the thread wound golf ball. For example, thethread rubber can be obtained by vulcanizing a rubber compositionprepared by formulating sulfur, a vulcanization aid, a vulcanizationaccelerator, an antioxidant and the like to a natural rubber or a blendrubber of the natural rubber and a synthetic polyisoprene. Athread-wound core can be produced by drawing the thread rubber about1000% and winding it over the center. However, such solid andthread-wound cores are given by way of illustrative examples only, andthe invention shall not be limited thereto.

[0023] In the golf ball of the present invention, the core has adiameter of 40.0 to 42.5 mm, preferably 40.3 to 42.0 mm. When thediameter of the core is smaller than 40.0 mm, the volume content of thecore is small based on the total volume of the golf ball, and therebound characteristics are degraded. On the other hand, when thediameter of the core is larger than 42.5 mm, the cover is too thin, andthe technical effects of improving the flyer resistance are notsufficiently obtained, or the durability is degraded.

[0024] The cover is then covered on the core. In the golf ball of thepresent invention, it is required for the cover to have a complexelastic modulus at −10° C. of 20 to 150 MPa and loss tangent (tan δ) at−10° C. of not less than 0.05, as determined from temperature-dependentcurves of the complex elastic modulus and tan δ obtained by dynamicviscoelastic measurement at a frequency of 10 Hz, a dynamic strain of 5%and a heating rate of 4° C./min.

[0025] The cover may have a single-layered structure or a multi-layeredstructure, which has two or more layers. The materials suitably used inthe cover of the present invention is not limited as long as the complexelastic modulus and tan δ are within the above ranges, but it is notsuitable to use ionomer resin alone, which is general cover material.Particularly, it is effective to use thermoplastic elastomer,ethylene-methacrylic acid copolymer, mixtures thereof with ionomer resinand the like, in order to accomplish high tan δ.

[0026] The thermoplastic elastomer is not limited as long as it iscomposed of soft segments having rubber elasticity and hard segments(such as a frozen phase or crystalline phase), which restrain plasticdeformation, but include polystyrene-based thermoplastic elastomer,polyamide-based thermoplastic elastomer, polyester-based thermoplasticelastomer, polyolefin-based thermoplastic elastomer, polyurethane-basedthermoplastic elastomer and the like. The thermoplastic elastomer hasonly low complex elastic modulus, but can have high tan 5 by selectingthe soft segments. Preferred are polystyrene-based thermoplasticelastomer. Examples thereof, for example, include SBS resin composed ofpolystyrene phase (S) and polybutadiene phase (B), SIS resin composed ofpolystyrene phase (S) and polyisoprene phase (B), SEPS resin composed ofpolystyrene phase (S) and ethylene/propylene phase (EP), SEBS resincomposed of polystyrene phase (S) and ethylene/butylene phase (EB) andthe like.

[0027] Examples thereof, which are commercially available, includestyrene-based thermoplastic elastomers commercially available from JSRCo., Ltd., under the trade name “TR” series (e.g., “TR2787”) and “SIS”series (e.g., “SIS5000”); styrene-based thermoplastic elastomerscommercially available from Asahi Chemical Industry Co., Ltd., under thetrade name “Tuftec” series (e.g., Tuftec Z514); styrene-basedthermoplastic elastomers commercially available from Kuraray Co., Ltd.,under the trade name “Septon” series (e.g., “Septon 2002”);styrene-based thermoplastic elastomers commercially available fromAronkasei Co., Ltd., under the trade name “AR” series (e.g., “AR790”);and the like.

[0028] Examples of ethylene-methacrylic acid copolymers, which arecommercially available, include ethylene-methacrylic acid copolymerscommercially available from Du Pont-Mitsui Polychemicals Co., Ltd.,under the trade name “Nucrel” series (e.g., “Nucrel AN4211”, “NucrelAN4213” and the like).

[0029] The polymer components for cover composition may use as mixtureswith the other cover materials having high rebound characteristics, suchas ionomer resin, but the thermoplastic elastomer is preferablycomprised in amount of not less than 30% by weight in the polymercomponents for cover composition.

[0030] The ionomer resin may be a copolymer of ethylene andα,β-unsaturated carboxylic acid, of which a portion of carboxylic acidgroups is neutralized with metal ion, or a terpolymer of ethylene,α,β-unsaturated carboxylic acid and α,β-unsaturated carboxylic acidester, of which a portion of carboxylic acid groups is neutralized withmetal ion. Examples of the α,β-unsaturated carboxylic acid in theionomer include acrylic acid, methacrylic acid, fumaric acid, maleicacid, crotonic acid and the like, preferred are acrylic acid andmethacrylic acid. Examples of the α,β-unsaturated carboxylic acid esterin the ionomer include methyl ester, ethyl ester, propyl ester, n-butylester and isobutyl ester of acrylic acid, methacrylic acid, fumaricacid, maleic acid, crotonic acid and the like. Preferred are acrylicacid esters and methacrylic acid esters. The metal ion which neutralizesa portion of carboxylic acid groups of the copolymer or terpolymerincludes a sodium ion, a potassium ion, a lithium ion, a magnesium ion,a calcium ion, a zinc ion, a barium ion, an aluminum, a tin ion, azirconium ion, cadmium ion, and the like. Preferred are sodium ions,zinc ions, magnesium ions and the like, in view of reboundcharacteristics, durability and the like.

[0031] The ionomer resin is not limited, but examples thereof will beshown by a trade name thereof. Examples of the ionomer resins, which arecommercially available from Du Pont-Mitsui Polychemicals Co., Ltd.include Hi-milan 1555, Hi-milan 1557, Hi-milan 1605, Hi-milan 1652,Hi-milan 1702, Hi-milan 1705, Hi-milan 1706, Hi-milan 1707, Hi-milan1855, Hi-milan 1856 and the like. Examples of the ionomer resins, whichare commercially available from Du Pont Co., include Surlyn 8945, Surlyn9945, Surlyn 6320, Surlyn AD8511, Surlyn AD8512, Surlyn AD8542 and thelike. Examples of the ionomer resins, which are commercially availablefrom Exxon Chemical Co., include Iotek 7010, Iotek 8000 and the like.These ionomer resins may be used alone or in combination.

[0032] The cover composition used in the present invention mayoptionally contain fillers (such as barium sulfate, etc.), pigments(such as titanium dioxide, etc.) and the other additives such as adispersant, a plasticizer, an antioxidant, a UV absorber, aphotostabilizer and a fluorescent agent or a fluorescent brightener,etc., in addition to the polymer component as a main component as longas the addition of the additives does not deteriorate the desiredperformance of the golf ball cover.

[0033] It is desired for the cover of the golf ball of the presentinvention to have a thickness of 0.3 to 3.5 mm, preferably 0.8 to 2.5mm. When the thickness is smaller than 0.3 mm, the technical effects ofimproving the flyer resistance are not sufficiently obtained, or thestrength is low, and the durability is degraded. On the other hand, whenthe thickness is larger than 3.5 mm, the volume content of the core issmall based on the total volume of the golf ball, and the reboundcharacteristics are degraded.

[0034] A method of covering on the core with the cover is notspecifically limited, but may be a conventional method. For example,there can be used a method comprising molding the cover composition intoa semi-spherical half-shell in advance, covering the core with the twohalf-shells, followed by press molding at 130 to 170° C. for 1 to 5minutes, or a method comprising injection molding the cover compositiondirectly on the core, which is covered with the cover, to cover it.

[0035] In the injection molding, when the thermoplastic elastomer isused, it is injected with flowable state by heating, followed bycooling, and then pulled out with solidified state. On the step ofmolding the cover composition into a semi-spherical half-shell in pressmolding, when the thermoplastic elastomer is used, it is injected withflowable state by heating, followed by cooling, and then pulled out withsolidified state as described in the injection molding.

[0036] At the time of molding the cover, many depressions called“dimples” may be optionally formed on the surface of the golf ball.Furthermore, paint finishing or marking with a stamp may be optionallyprovided after the cover molded for commercial purposes. Factors, whichhave an effect on the shape and surface of the cover, have an effect onthe friction force and spin of the golf ball when the golf ball directlycontacts with the golf club face, but have no effect on the flyerresistance when putting the grass between the golf club face and thegolf ball. The golf ball of the present invention is formed, so that ithas a diameter of not less than 42.67 mm (preferably 42.70 to 43.20 mm)and a weight of not more than 45.93 g, in accordance with theregulations for golf balls.

[0037] In the golf ball of the present invention after covering with thecover, it is desired to have a compression (a deformation amount, whenapplying from an initial load of 98 N to a final load of 1275 N) of 2.2to 4.5 mm, preferably 2.5 to 3.3 mm, more preferably 2.9 to 3.2 mm. Whenthe deformation amount is smaller than 2.2 mm, the golf ball is toohard, and the shot feel is poor. On the other hand, when the deformationamount is larger than 4.5 mm, the golf ball is too soft, and the reboundcharacteristics are degraded, which reduces the flight distance.

EXAMPLES

[0038] The following Examples and Comparative Examples furtherillustrate the present invention in detail but are not to be construedto limit the scope of the present invention.

[0039] Production of Core

[0040] The rubber composition for the core having the formulation shownin Table 1 was mixed, and then vulcanized by press-molding at 155° C.for 18 minutes in the mold to obtain spherical solid core having adiameter of 38.5 mm. TABLE 1 Amount Core composition (parts by weight)Polybutadiene *1 100 Zinc acrylate 33 Zinc oxide 9.7 Barium sulfate 9.7Dicumyl peroxide 1.0 Antioxidant *2 0.2

[0041] Preparation of cover compositions

[0042] The formulation materials showed in Table 2 were mixed at 160 to180° C. using a kneading type twin-screw extruder to obtain pelletizedcover compositions. The extrusion condition was,

[0043] a screw diameter of 45 mm,

[0044] a screw speed of 200 rpm,

[0045] a screw L/D of 35, and

[0046] a cylinder temperature of 210° C.

[0047] With respect to the resulting cover composition, a complexelastic modulus and tan δ at −10° C. was determined by dynamicviscoelastic measurement. The result is shown in Tables 3 and 4. TABLE 2(parts by weight) Exam- Cover ple No. Comparative Example No.composition 1 2 1 2 3 4 5 6 7 AR790 *3 70 — 100 — — — — — — Nucrel — 50— 100 — — — — — AN4213 *4 Nucrel — — — — 100 — — — — AN4311 *5 Hytrel —— — — — 100 — — — 4047 *6 Elastollan — — — — — — 100 — — ET850 *7Hi-milan 30 50 — — — — — 100 — 1706 *8 Septon — — — — — — — — 100 2002*9

Examples 1 to 2 and Comparative Examples 1 to 7

[0048] The cover compositions were covered on the core obtained asdescribed above by injection molding. Then, deflashing, surfacepretreatment for painting, paint and the like, which are generally doneon the surface of a golf ball, were conducted on the surface to producea two-piece solid golf ball having a diameter of 42.7 mm. With respectto the resulting golf balls, the flight distance, compression(deformation amount) and flyer resistance were measured or evaluated.The results are shown in Tables 3 and 4. The test methods are asfollows.

[0049] (Test Method)

[0050] (1) Dynamic Viscoelastic Measurement

[0051] A specimen of 4 mm (width)×30 mm (length)×0.5 mm (thickness)prepared from the cover composition is forcibly vibrated using aviscoelastic spectrometer DVA 200 type, manufactured by Shimadzu Co. atthe following conditions, to measure a vibration amplitude ratio and aphase lag between drive part and response part, wherebytemperature-dependent curves of a complex elastic modulus and tan 5 wereobtained.

[0052] Deformation mode: simple stretching (in the direction of thelength)

[0053] Frequency: 10 Hz

[0054] Dynamic strain: 5% (0.2 mm)

[0055] Measuring temperature range: −50 to 50° C.

[0056] Heating rate: 4° C./min

[0057] The values of the complex elastic modulus at −10° C. and tan δ at−10° C. determined from the temperature-dependent curves are shown asthe complex elastic modulus and tan 5 of each cover. (2) FlightPerformance

[0058] A No. 1 wood club (W#1, a driver) was mounted to a swing robotmanufactured by True Temper Co. and the resulting golf ball was hit at ahead speed of 45 m/sec, the flight distance was measured. As the flightdistance, carry that is a distance to the dropping point of the hit golfball was measured. The measurement was conducted by using 8 golf ballsfor every sample (n=8), and the average is shown as the result of thegolf ball. (3) Ball Compression

[0059] The ball compression is determined by measuring a deformationamount, when applying from an initial load of 98 N to a final load of1275 N on the golf ball. (4) Flyer Resistance

[0060] At approach shot using a pitching wedge, the spin amount (P₁)when commonly hit in the state of teeing up, and the spin amount (P₂)when hit from a rough 4 cm in depth were measured, and the flyerresistance was determined by calculating the ratio (P₂/P₁×100). When thevalue is smaller, the golf ball is easier to occur the flyer. On theother hand, when the value is larger, the golf ball is more difficult tooccur. The measurement was conducted by 10 high-level golfers accordingto practical hitting test, and the average is shown as the result of thegolf ball.

[0061] (Test Results) TABLE 3 Example No. Comparative Example No. Testitem 1 2 1 2 3 (Cover) Complex elastic 29.4 49.0 9.8 14.7 2.9 modulus(MPa) Tan δ 0.07 0.11 0.12 0.18 0.22 (Golf ball) Flight distance (m) 204206 200 201 191 Compression (mm) 3.14 2.96 3.55 3.31 3.70 Flyerresistance 66 64 67 67 68

[0062] TABLE 4 Comparative Example No. Test item 4 5 6 7 (Cover) Complexelastic 5.9 2.0 68.6 16.2 modulus (MPa) Tan δ 0.03 0.05 0.04 0.15 (Golfball) Flight distance (m) 199 190 207 201 Compression (mm) 3.64 3.782.85 3.26 Flyer resistance 30 65 32 66

[0063] As is apparent from the results of Tables 3 to 4, the golf ballsof the present invention of Examples 1 to 2, which adjust the complexelastic modulus and tan δ of the cover to specified ranges, haveexcellent flyer resistance and long flight distance, when compared withthe golf balls of Comparative Examples 1 to 7.

[0064] On the other hand, in the golf balls of Comparative Examples 1 to3 and 7, the flyer resistance is excellent because the cover has largetan δ, but the complex elastic modulus of the cover is small, and theflight distance is short. In the golf ball of Comparative Example 4, thecomplex elastic modulus of the cover is small, and the flight distanceis short. In addition, the tan δ is small, and the flyer resistance ispoor.

[0065] In the golf ball of Comparative Example 5, the flyer resistanceis excellent because the tan δ of the cover is large, but the complexelastic modulus of the cover is small, and the flight distance is short.In the golf ball of Comparative Examples 6, the flight distance is longbecause the complex elastic modulus of the cover is large, but the tan δof the cover is small, and the flyer resistance is poor.

What is claimed is:
 1. A golf ball comprising a core having asingle-layered structure or a multi-layered structure and a covercovering the core, wherein the cover has a complex elastic modulus at−10° C. of 20 to 150 MPa and a loss tangent (tan δ) at −10° C. of notless than 0.05, as determined from temperature-dependent curves of thecomplex elastic modulus and tan δ obtained by dynamic viscoelasticmeasurement at a frequency of 10 Hz, a dynamic strain of 5% and aheating rate of 4° C./min.
 2. The golf ball according to claim 1,wherein the cover comprises 30% by weight of thermoplastic elastomer ina base polymer.
 3. The golf ball according to claim 1 or 2, wherein thecover is formed from materials selected from the group consisting ofthermoplastic elastomer, ethylene-methacrylic acid copolymer andmixtures thereof with ionomer resin.